CH. XXXYIII.] EXTIKPATION OF THE KIDNEYS 579 



the part of the theory which deals with reabsorption we have seen 

 reasons for not accepting. 



The general appearance of the capsular epithelium resembles 

 that lining a lymph space, and some morphologists hold the view 

 that each capsule is in development part of the peritoneum, whilst 

 others regard it as part of the kidney tubule. It is possible 

 that the glomerulus has other functions besides that of a filter. 

 Brodie, for instance, has suggested that its main, if not its 

 only use is that of a driving force to propel the secreted urine 

 along the tubule, the resistance of which is very great; he has 

 invented models which demonstrate that pulsations of the kind 

 alleged to occur in the glomeruli will drive fluid along a tube ; 

 he further supports his theory by the observation that the maximum 

 pressure in the ureter as measured by a manometer is usually at 

 least 30 to 44 mm. of mercury less than the arterial blood-pressure, 

 and is probably equal to the pressure in the glomerular capillaries. 

 But these views have not at present been fully accepted by the 

 majority of physiologists. 



Bowman's classical theory was formulated more than seventy 

 years ago, that is, long before many of the experiments just described 

 were performed. It accords much more nearly with modern views 

 than that of Ludwig, and was founded mainly as a deduction from 

 anatomical structure, namely, the histological appearances of the 

 epithelial cells which line the tubules, and the double vascular 

 supply which in the frog indicates that the work of the tubule is 

 distinct from that of the glomerulus. He considered that the cells 

 lining the capsule have much the same function as those lining a 

 lymph space, and that it is the glandular epithelium of the tubules 

 which secretes the nitrogenous constituents of the urine. We may 

 accept the last part of the theory as now definitely proven. But 

 whether the glomerular flow is conditioned by physical or by 

 physiological factors is the main point at issue between investigators 

 at present. In the minds of both Ludwig and Bowman the physical 

 factor was uppermost. Heidenhain, and more recently Brodie, regard 

 the flat glomerular cells as true secreting cells. Our own view is 

 that although active secretion on the part of these cells has not 

 been proved to exist, the possibility cannot be altogether denied, 

 and as will be gathered from what has preceded this, our bias is 

 distinctly in favour of the physical or filtration hypothesis. 



Extirpation of the Kidneys. 



Extirpation of one kidney for stone, etc., is a common operation. 

 It is not followed by any untoward result. The remaining kidney 

 enlarges and does the work previously shared between the two. 



